In lithographic printing, a printing blanket is employed to transfer printing ink from the printing plate to the article being printed, such as paper, plastic or metal films, or other such materials.
Compressible printing blankets are normally employed on high speed, multicolor web presses to allow for maximum print sharpness and operating latitude. In order to provide good register control, that is, the relative placement of the various colors to one another, it has been found necessary to employ a stabilizing layer between the compressible layer and the top, ink transfer surface rubber layer. The stabilizing layer may be either a textile fabric layer and/or a high modulus rubber film. See, for example: U.S. Pat. No. 1,327,757 to Dunkley; U.S. Pat. No. 1,327,758 to Dunkley et al.; U.S. Pat. No. 3,700,541 to Dunkley et al., issued Oct. 10, 1972; U.S. Pat. No. 4,471,011 to Sporing, issued Sept. 11, 1984; U.S. Pat. No. 4,042,743 to Larson et al., issued Aug. 16, 1977; U.S. Pat. No. 4,061,818 to Duckett et al., issued Dec. 6, 1977; and, U.S. Pat. No. 4,770,928 to Gaworowski et al., issued Sept. 13, 1988. The use of a hard rubber layer to provide the required dimensional stability has been taught by U.S. Pat. No. 1,327,758 to Dunkley; U.S. Pat. No. 1,327,758 to Dunkley et al.; U.S. Pat. No. 4,303,721 to Rodriguez, issued Dec. 1, 1981; and, U.S. Pat. No. 4,812,357 to O'Rell et al., issued Mar. 14, 1989.
The use of a fabric layer between the ink transfer surface layer and the compressible layer has provided the desired level of register control and web feed necessary for today's high speed presses, normally operating in excess of 1,500 feet per minute. However, a major problem encountered in using blanket constructions which contain fabric between the surface rubber layer and the compressible layer is a phenomena referred to as "fall-off at the gap". This is the result of the top reinforcing fabric having insufficient stretch to accommodate the change in geometry when the blanket is tucked into the cylinder gap and tightened. The fall-off at the gap results in a loss of print at the end or beginning of a page, which is deemed to be unacceptable to commercial printers. From a geometrical perspective, it can be seen that the closer the fabric reinforcing layer is to the surface of the blanket, the greater its length has to be in order to accommodate being tucked into the cylinder gap without a corresponding loss in caliper. In many commercial constructions currently used today, surface rubber thicknesses range from 0.012-0.016 inches in order to reduce the path length of the top stabilizing fabric and thus minimize the fall-off at the gap phenomena.